KR20010052085A - Magnetic tap changer - Google Patents

Abstract

Induction control voltage regulators for high voltage regulation include a magnetic circuit based core having one or more flux paths or legs 2 surrounded by high voltage windings and low voltage windings 3, 15. The leg 2 is divided into at least two branches 2A and 2B, at least one of which branches 2B has an adjustment device with a calibrated permeability zone 5. Permeability correction is made by a magnetic rod 4 which is actuated with respect to the zone 5 formed as an air gap. Another embodiment for such calibration involves the use of regulator windings to adjust the magnetic flux through the leg branches. A compensating winding can be arranged around the leg branch 2B which includes the correctable permeability zone 5. The compensation winding is connected in series with the capacitor means. At least one winding is wound by a high voltage gable comprising a conductor wrapped by an internal semiconductor, an insulator and an external semiconductor.

Description

Magnetic Tap Changer {MAGNETIC TAP CHANGER}

Conventional induction control voltage regulators in the low voltage range are arranged using inductors having coils that are rotated or shifted relative to one another. La Core and K. Frey-Hahnsen, "Rotating Transformers and Trust Transformers, Exchange Technology Vol. 2, Transformers", Julius Springer Press, Berlin, Germany, 1936, pp. 568-598. Also, the induction control cannot be applied to high voltage at a reasonable cost. Insulation construction has strict design limitations.

Another technique is known from US-A-4 206 434, where the magnetic flux between different legs of the induction control voltage regulator is described as redistributed by variable DC magnetization. This requires a variable DC source.

Thus, high voltage control is mostly made of a transformer that includes one or more windings wound on one or more legs of the transformer iron core. The winding includes a tab that can supply different voltage levels from the transformer. The above-described current power transformers and distribution transformers used in voltage relay lines include a tap changer for voltage regulation. They are either mechanically worn or electrophysically corroded due to the discharge between the contacts. Adjustment is only possible in stages. Thus, stepwise voltage regulation and actuation contacts are required to make contact with the various taps.

The invention relates to inductance adjustment by an induction control voltage regulator, in particular by means of a transformer or reactor means as defined in claim 1. The invention also relates to a regulator winding for use in an inductively controlled voltage regulator as defined in claim 10 and a method for voltage control in an electrical line or reactive power control in a mechanical installation as defined in claim 13. It is about.

1 is a cross-sectional view of a portion of a transformer core according to the present invention.

2 shows a portion of a transformer core, partially shown in cross section, in accordance with one embodiment of the present invention.

3 is a view similar to FIG. 2 showing another embodiment of the present invention.

4 is a cross-sectional view of a high voltage cable used in the regulating winding according to the invention.

The disadvantages of conventional voltage regulation are overcome by the induction control voltage regulator according to the present invention. One of the features of the present invention is that the short magnetic flux path or leg length of the magnetic circuit wrapped by the high voltage and low voltage windings is divided into at least two branches, the at least one branch comprising an adjustment device having a calibrated permeability zone. .

A preferred embodiment of the regulator of the present invention has a high voltage winding wound wide to include all of the core magnetic flux. The low voltage winding of the regulator is divided into at least two winding parts, one winding part comprising most of the turns and wound inside the high voltage winding. Another winding portion comprising a few turns is wound around at least one leg branch with a calibrated permeability zone. The number of turns of the leg branch depends on the required voltage regulation range.

The required flux splitting between the different leg branches is achieved by changing the magnetoresistance of the different leg branches, which is realized by the correctable permeability zone. Other embodiments are possible within the scope of the invention. The most preferred embodiment is to include a regulator rod wound around a magnetic rod that is movable relative to a zone formed as an air gap or a separate magnetic core that forms a transverse path in a leg branch comprising the zone. The regulator winding is supplied with a control voltage that affects the magnetic flux through the leg branch.

The high magnetoresistance in the air gap can be compensated by a compensation winding which is enclosed in the zone and connected in series with the capacitor as a separate closed circuit.

Such a compensation winding loaded by a capacitor forms a negative magnetoresistance R _C = −n ² ω ² C. The adjustment of the number of turns turns n and the capacitance C of the capacitor are selected such that the positive magnetoresistance R _L = I / Aμ ₀ of the air gap, where

I is the (effective) length of the air gap,

A is the cross-sectional area of the magnetic core,

μ ₀ is the transmission of air.

Typical capacitance value C is from a few microfarads to a few milliparads for a voltage of about 1 kV.

The condition for enabling high voltage regulation of 36 to 800 kV is that at least part of any of the foregoing windings must be made of a high voltage cable comprising a conductor, an internal semiconductor, an insulator and an external semiconductor. Thus, the transformer / reactor is of the so-called "dry" type. By using a high voltage cable designed as above, it is possible to "capture" the electric field inside the cable insulator. This means that inductively controlled voltage regulators can be designed for high voltages.

A further advantage is that the layers are arranged to adhere to each other even when the cable is bent. This makes it possible to maintain good contact between layers during the entire cable life.

It is apparent to one skilled in the art that other uses are also within the scope of the present invention. Thus, for example, it is possible to apply the present invention to a single phase induction control voltage regulator. It is also possible to implement an on-load tap changer device, i.e., a single phase induction controlled voltage regulator integrated in a transformer. In addition, the multi-phase induction control voltage regulator can be made by individual phase control and common phase control.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

The invention is described with reference to some preferred embodiments, the principles of which are shown in the accompanying drawings. The same member denoted the same reference number. 1 and 2 show only a part of the voltage regulator which is an important part of the present invention.

1 shows a transformer core 1 of a core flux path or leg 2, with half of the core divided into two branches 2A, 2B. The high voltage winding 3 surrounds the undivided half of the leg 2 at an external position, in which the first portion 15A of the low voltage winding is wound around the leg 2. The winding is shown in cross section. The first portion 15A of the low voltage winding includes most of the winding turns and is connected in series with the second portion 15B of the low voltage winding. The second part 15B with a slight winding turn surrounds one of the leg branches 2B.

The voltage regulation of the transformer is based on the principle of changing the magnetic flux Φ coupling in the transformer windings by controlling the magnetic resistivity of the different core leg branches 2A, 2B. To this end, one or two core leg branches may comprise an area 4 in which the permeability is increased and / or decreased by the control means.

Figure 2 shows a preferred embodiment of the invention, where the legs 2 of the transformer core 1 are wrapped by the (main) first part 15A of the high voltage winding 3 and the low voltage winding. In other words, the leg is divided into two branches 2A and 2B at the top. In the embodiment shown in FIG. 1, the second portion 15B of the low voltage winding is wound around the leg branch 2B. This leg branch 2B comprises an air gap 5 in which a magnetic rod 4 is arranged. The rod 4 is movable relative to the air gap 5 as indicated by the double arrow A. FIG. The movement of the magnetic rod 4 can be controlled manually or by means of suitable mechanical means by electric drive means. By moving the magnetic rod 4 the magnetic flux in the second portion 15B of the low voltage winding can be varied between zero and maximum core branch magnetic flux. The number of turns of winding of the second portion 15B of the low voltage winding defines a regulating area.

As shown by the dashed line in FIG. 2, the other leg branch 2A may also include an air gap 5 with a movable rod 4. By using such a rod 4 in the two leg branches 2A, 2B, a more precise magnetoresistance in the core 1 can be adjusted. The movement of the rods 4 can be combined directly or from each other. The initial position of the rod 4 of the air gap 5 may be different. For example, the rod of leg branch 2B can completely fill the air gap (as shown in FIG. 2), while at the same time the rod of leg branch 2A can be placed somewhat outward with respect to the corresponding air gap. have.

Another embodiment of the invention is shown in FIG. 3, where the mechanical rod and air gap are replaced by an external magnetic field. Such external magnetic field is obtained by a separate magnetic core 9, the axis of which is arranged transverse to the axis of the leg branch 2B. The magnetic core 9 may be a premagnetized section or a core preferably wrapped by the regulator winding 6. The external magnetic field generated by the regulator winding 6 and / or the separate magnetic core 9 somewhat interferes with the magnetic flux through the leg branch depending on the control voltage supplied to the regulator winding 6. The control voltage may be an AC voltage or preferably a DC voltage in phase with the voltage to be adjusted. The same induction control voltage of the transformer or reactor is obtained by this embodiment as shown in Figs.

As shown in FIG. 2, the compensating winding 7 is wound around the flux path or leg 2 of the transformer core 1. The compensation winding 7 forms a closed circuit comprising a capacitor means 8.

The compensation circuit described may be implemented in the embodiment shown in FIG. 3.

In order to enable high voltage (i.e., about 36 to 800 kV) adjustment, at least one winding 3, 6, 7, 15A, 15B, or a portion thereof, is, for example, a high voltage cable 61 in the form shown in FIG. Wound using).

The cables used in the present invention are flexible and of the end described in detail in WO 97/45919 and WO 97/45847. Further description of the cables involved is disclosed in WO 97/45918, WO 97/45930 and WO 97/45931.

Thus, the winding of the device according to the invention is preferably of a type corresponding to a cable with a solid extrusion insulator of the type used for power distribution, such as XLPE cables or EPR insulated cables. The cable includes an inner conductor composed of one or more strands, an inner semiconductor layer surrounding the conductor, a solid insulating layer surrounding the first inner semiconductor layer, and an outer semiconductor layer surrounding the insulating layer. Such a cable is flexible and this property is important because the technique for the device according to the invention is based on a winding system in which the winding is formed of a cable which bends during assembly. The flexibility of the XLPE cable corresponds to a radius of curvature of about 20 cm for a cable with a diameter of 30 mm and to a radius of curvature of about 65 cm for a cable with a diameter of 80 mm. In the present application, the term “flexible” is used to exhibit a property that is liable to bend well with a radius of curvature of about 4 times the cable diameter, preferably 8 to 12 times the cable diameter.

The windings must retain their properties when they are bent and under thermal or mechanical stress during operation. In this relationship it is important for the layers to maintain adhesion to each other. The mechanical properties of these layers, in particular elasticity and thermal expansion relative coefficients, are important. For example, in XLPE-cables, the insulating layer consists of crosslinked low density polyethylene and the semiconductor layer consists of polyethylene mixed with soot and metal particles. Volume changes due to temperature fluctuations are fully absorbed by cable radius changes, and due to the relatively small difference between the thermal expansion coefficients of the layers with respect to the elasticity of these materials, radial expansion can be achieved without loss of adhesion between the layers.

The foregoing material compounds are merely examples. Other compounds that meet the above conditions and other compounds that satisfy semiconductor conditions that basically have a resistance within 10 ^-1 -10 ⁶ ohm-cm, for example 1-500 ohm-cm or 10-200 ohm-cm It falls within the range of.

Insulation layers are for example solid thermoplastics such as low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polybutylene (PB), polymethyl pentene ("TPX"), crosslinked polyethylene (XLPE) Cross-linked material such as) or rubber such as ethylene propylene rubber (EPR) or silicone rubber.

The inner and outer (first and second) semiconductor layers may be made of the same base material but may be composed of conductive particles in which soot or metal powder is mixed.

The mechanical properties of these materials, in particular the coefficient of thermal expansion, are relatively less affected by the presence of soot or metal powder (at least in proportions necessary to achieve conductivity according to the invention). Thus, the insulating layer and the semiconductor layer have similar coefficients of thermal expansion.

Ethylene-vinyl-acetate copolymer / nitride rubber (EVA / NBR), butyl graft polyethylene, ethylene-butyl-acrylate copolymer (EBA) and ethylene-ethyl-acrylate copolymer (EEA) are also incorporated into the semiconductor layer. Constitute a suitable polymer.

Although different kinds of materials are used as the base of the various layers, their coefficient of thermal expansion is preferably the same. This is the case with the substances listed above.

The above listed materials have a relatively good shrinking force, E-modulus of E <500 MPa, preferably E <200 MPa. The shrinking force is such that the minimum difference between the coefficients of thermal expansion for the material in the layer is sufficient to be absorbed by the radial shrinking force so that no cracking or any damage occurs and the layers do not separate from each other. The material in the layers is elastic and the adhesion between the layers should be at least the same size at the weakest part of the material.

The conductivity of the two semiconductor layers is sufficient for the potential along each layer to be the same. The conductivity of the outer semiconductor layer should be high enough to cover the electric field in the cable but low enough so that no losses are caused by the current induced in the longitudinal direction of the layer.

Thus, each of the two semiconductor layers constitutes one equipotential surface and these layers surround the electric field between them.

Of course, it is also possible for one or more additional semiconductor layers to be arranged in the insulating layer.

The high voltage gable 61 as described above may include one or more electrical conductors 631. The cable embodiment shown in FIG. 4 includes an insulator, and the conductor 631 is directly connected with the first layer 632 having semiconductor properties. The first layer 632 is wrapped by the solid insulating layer 633, and the insulating layer is wrapped by the second layer 634 having semiconductor properties.

In FIG. 4, which shows the details of the present invention for the cable, the three layers 632, 633, 634 are arranged to adhere to each other even when the cable is bent. The cable shown is flexible and this property is maintained for the entire cable life.

Preferably, layers 632, 633, 634 are made of the same plastic material or materials with the same coefficient of expansion. Thereby, an important advantage can be obtained, which is that defects, cracks and the like in the thermal fluctuation of the winding can be prevented. An electrically conductive material is added to the plastic material of the first and second layers 632 and 634.

Although the present invention has been described with reference to the transformer or reactor shown in the figures as a single phase, it can be applied to polyphase transformers and similar devices, such as automatic transformers and booster transformers.

Claims (17)

In an inductively controlled voltage regulator such as a transformer or a reactor comprising a magnetic circuit wrapped by a high voltage winding and a low voltage winding 3, 15 and having a core 1 with at least one flux path or leg 2, The length of the at least one leg 2 is divided into at least two branches 2A, 2B, at least one of which branches has an adjustment device 4 or 6 with a calibrated permeability zone 5, and a high voltage At least one turn of the winding 3 is wound with a high voltage cable 61 comprising a conductor 631, an internal semiconductor 632, an insulator 633, and an external semiconductor 634. . 2. The high voltage winding (3) according to claim 1, wherein the high voltage winding (3) is wound away to include all core magnetic flux, and the low voltage winding (15) is divided into at least two winding portions (15A, 15B), the winding portion (15A). Includes most of the turns and is wound inside the high voltage winding 3, the other winding portion 15B comprising a few turns, around at least one leg branch 2B with a calibrated permeability zone 5. Induction control voltage regulator, characterized in that the winding on. Induction control voltage regulator as claimed in claim 1, characterized in that the correctable permeability zone (5) comprises a magnetic rod (4) movable relative to the zone (5) formed as an air gap. The at least one leg branch according to claim 1 or 2, wherein the correctable permeability zone (5) is wound on a separate magnetic core (9) forming a transverse path with respect to the at least one leg branch (2B). Induction control voltage regulator, characterized in that it comprises a regulator winding (6) provided with a control voltage for control of the magnetic flux passing through (2B). Induction control voltage regulator according to any of the preceding claims, characterized in that it comprises a compensating winding (7) in series with the capacitor means (8) surrounding the area of the calibrated permeability zone (5). The high voltage cable according to any one of the preceding claims, wherein at least one additional winding (6, 7, 15A, 15B) comprises a conductor (631), an internal semiconductor (632), an insulator (633) and an external semiconductor (634). Induction control voltage regulator, characterized in that winding to 61). The method according to any one of the preceding claims, characterized in that the regulator is a polyphase transformer, wherein the at least one leg branch (2B) of each phase comprises an adjusting device (4 or 6) to independently adjust each phase. Induction control voltage regulator. 7. The regulator according to any one of the preceding claims, characterized in that the regulator is a polyphase transformer, and wherein the at least one leg branch (2B) of each phase comprises an adjustment device (4 or 6) connected for joint adjustment. Induction control voltage regulator. The inductively controlled voltage regulator according to any one of claims 1 to 6, wherein said regulator is an automatic transformer or a booster transformer. The inductively controlled voltage regulator as claimed in claim 1, wherein the layers (632, 633, 634) are arranged to adhere to each other even if the cable is bent. In a regulator winding for an inductively controlled voltage regulator such as a transformer or a reactor comprising a high voltage winding 3 and a low voltage winding 15A, 15B according to any one of the preceding claims, At least one of the windings 3, 6, 15A, 15B or part of one of these high voltage gables 61 includes a conductor 631, an internal semiconductor 632, an insulator 633, and an external semiconductor 634. Regulator reel, characterized in that coiled by. 12. The regulator winding of claim 11 wherein the semiconductor (632, 634) and the insulator (633) have the same coefficient of expansion. 13. The regulator winding as claimed in claim 11 or 12, wherein the semiconductor (632, 634) and the insulator (633) are made of the same plastic material, and a conductive material is added to the semiconductor plastic material. A method for voltage control of an electrical line and / or reactive power control in an electrical installation comprising at least one transformer or reactor, The transformer or reactor has a portion of at least one winding or winding consisting of a high voltage gage according to any of the preceding claims, wherein the voltage control induces a change in magnetic flux such that the magnetoresistance of the different leg branches of the transformer / reactor is changed. Characterized by the adjustment. 15. The method of claim 14, wherein the induction adjustment is achieved by moving a magnetic rod relative to an air gap in at least one of the different leg branches. 15. The method of claim 14, wherein the induction regulation is achieved by varying the regulation voltage supplied to the winding wound around the regulation leg of the transformer / reactor. 17. The method of claim 16, wherein changing the regulated voltage is made by controlling a capacitor having controllable capacitance.